1. Field of the Invention
This invention relates to spectrometry and more particularly relates to an apparatus, system, and method for label-free quantitative detection of biomarkers.
2. Description of the Related Art
Biomarker detection plays an important role in the diagnosis of various diseases, life science research and drug discovery. Detection and quantification of these biomarkers have the potential of improving and expediting drug development, treatment planning, and prediction of reoccurrence of various diseases. It can provide an important diagnostic tool at the molecular level. For example, cancer cells typically over express biomarkers as compared to their non-tumorogenic counterparts. Hence, the quantification of biomarkers often plays an important role in differentiating cancerous cells from non-cancerous cells.
Additionally, current methods for studying protein-analyte interactions or detecting a specific protein include enzyme-linked immunosorbent assays (ELISA) and western blotting. These long established techniques, however, need secondary probes for detection of analytes that may alter the protein of interest, are relatively costly, and require extensive sample preparation. On the other hand, researchers are exploring different label-free techniques for the detection and quantification of protein-analyte interaction. Some of the techniques explored are Isothermal Titration Calorimetry (ITC), Differential Scanning calorimetry (DSC), and ellipsometry imaging, among others. Using these techniques, binding affinity of analyte to protein, kinetic characterization, and protein quantization can be achieved.
The detection and quantification of large and small molecules is necessary in a wide variety of fields ranging from biosensing to screening of biomolecules in the drug discovery process. Currently, the technologies that are predominantly used in practice are label-based in which biomolecules to be screened are labeled with fluorescent, radioisotope, or chemiluminescent tags. Inherent limitations of labels are widely acknowledged, the most important of which center on their potential interference with the activity of the biomolecule and its interaction with the recognition molecule, along with the added costs involved in developing and implementing the label attachment chemistry. Furthermore, direct quantification of interactions and concentrations are not possible using labeled methods. Label-free detection and quantification of bimolecular interaction has significant advantages, such as lack of interference from labels, higher accuracy and less expensive assays. Until recently, surface plasmon resonance (SPR) was perhaps the only reliable and widely used label-free technique due to the sensitivity and commercial availability of the instrumentation. But, for multi-analyte detection, SPR has achieved limited success.
In recent years a number of promising label-free techniques have been developed that have the potential to be the method of choice for a number of biomolecular interaction analysis applications. Using label-free optical techniques, either the change in refractive index (RI) or the change in optical path length (OPL-a product of geometric length and RI) that occurs when biomolecules bind to the target is measured. Changes in RI or OPL can be accurately measured with optical techniques such as interferometry and SPR. Besides detection sensitivity, high throughput is necessary and is an important figure of merit for many biosensing applications. Limited throughput capability is a drawback of typical label-free techniques such as SPR. Although high throughput label-free detection of biomolecules has been demonstrated using spin-disk interferometry and spectral reflectance imaging of biosensor arrays, these techniques are limited to fixed biosensor formats with custom fabricated biosensor substrates.